1. Field of the Invention
This invention relates to a device for adjusting eccentric value of a crank portion in a press machine.
2. Description of the Related Art
Devices for adjusting the eccentric value of a crank shaft to alter the slide stroke in a press machine are known. A conventional device of this type employs an eccentric sleeve.
A crank pin is utilized in eccentric portion eccentric from the rotating axis of a crank shaft, to which the eccentric sleeve is rotatably accompanied. One end portion of a connecting rod is rotatably coupled to the outer circumference of the eccentric sleeve. A fixing means for positioning the eccentric sleeve with reference to the crank pin is also provided. In this prior art structure, an adjustment of eccentric value of slide stroke, or the crank portion can be done by controlling a relative angle of the eccentric sleeve to the crank pin. The one end portion of the connecting rod eccentric from the rotating axis of the crank shaft via the crank pin and eccentric sleeve can alter its portion from rotating axis, so that adjustment of eccentric value can be performed.
It is known that Japanese Utility Model Application No. 63-6200 shows a device for adjusting eccentric value without rotating an eccentric sleeve (eccentric sheave). In this device, the sheave does not rotate and a straight angle rotation is done by a reciprocal shift of a lock pin between the eccentric sheave and the eccentric portion of the crank shaft.
However, the mentioned conventional eccentric value adjusting device making use of the rotatable eccentric sleeve should result in deviation of eccentric value and the properties of slide movement or the crank motion. This is because when the eccentric sleeve rotates in regard to the crank pin, the one end portion of the connecting rod does not only deviate from axis of the crank shaft to the eccentric direction of the crank pin, but another direction meeting at right angles thereto.
As mentioned above, when the crank motion undergoes changes, fine pressing cannot be expected and it should be influential in producing products.
While in the latter eccentric value adjusting device, it does not have changes of the crank motion but limits its adjustability in two-mode stroke, which is not useful.
It is generally known that if the crank shaft has a balance weight, an eccentric value adjustment in a press machine needs another adjustment where an eccentric connecting portion of the balance weight. However, no effective eccentric value adjusting device for the eccentric portion of the balance weight is proposed, so that an applicable eccentric value adjusting device to the balance weight is expected to be provided in the market.
An object of the present invention is to provide an eccentric value adjusting device for the eccentric portion of the crank shaft in a press machine, which should not badly influence the crank motion of the slide when adjusting the eccentric value of the crank portion of a press machine.